new Species o/'Clementia. 59 



were included in a small set of different species of Caryatis 

 ( = Pitaria), and were accompanied by a ticket bearing the 

 inscription " Caryatis aresta, Dall and Simpson, Mayaguez, 

 Porto Rico." Knowing that I was then making a study of 

 the genus Pitaria, Mr. Melvill very kindly sent me one of 

 these shells, together with some of the other species, for 

 examination, which revealed the fact that the supposed 

 " Pitaria aresta" did not belong to that species or genus, 

 but were a form of dementia. 



So far as external appearance is concerned, the shell does 

 closely resemble P. aresta as figured and described by 

 Messrs. Dall and Simpson, and Porto llico is the locality 

 from which that species was obtained. Both are inflated 

 shells of a dull white colour, with fine concentric striation, 

 obliquely oblong in shape, with rather prominent umbones 

 set far forward, so that there is a short anterior and a very long 

 posterior slope. But the hinge of the shell hereafter described 

 is very different from that of Pitaria, being without any 

 lateral teeth, and having a deep triangular concavity in front 

 of each anterior cardinal. 



The special interest of this discovery lies in the fact that 

 all the known recent species of dementia are inhabitants of 

 the Indian and Pacific Oceans, whereas this comes from the 

 Caribbean Sea. There is no reason to doubt the accuracy of 

 the label, which appears to be in the late Mr. Billow's hand- 

 writing, nor is there any reason to suppose that this label 

 had been interchanged with some other one, for none of the 

 other species in the set resemble P. aresta, while these two 

 shells might have been mistaken for that species by anyone 

 who did not critically examine them inside. 



I have compared the specimen in my hands with the figures 

 and descriptions of all the known species of dementia, and, 

 further, by the kindness of Mr. J. J. Mac Andrew 1 have had 

 the opportunity of actually seeing specimens of most of the 

 species, and I rind the shell in question to be different from 

 all of them. It is a stouter, stronger, and more chalky shell 

 than any of the recent species, so that the interior has a 

 smooth surface of its own, which is not the counterpart of 

 the exterior, as in most recent species. 



The only modern species to which it bears any resemblance 

 is dementia vathelefi, Mabille, from Korean waters. I am 

 indebted to Mr. G. K. Gude for sending me a copy of 

 Mabille's description of this species, which was not accom- 

 panied by a figure*; from this Latin description C. vatheleti 



* Bull. Soc. Philom. Paris, (8) iii. p. 57 (1001). 



